1. Field of the Invention
The invention relates to a drive device for an adjustable vehicle mirror, using a self-calibrating potentiometer, as well as to a self-calibrating potentiometer.
2. Discussion of Related Art
Drive devices for adjusting a rear-view mirror are known, for example from WO 98/31565, by means of which the rear-view mirrors are adjusted. In top-of-the-range automobiles, when the driver changes, not only the position of the driver""s seat but also the position of the rear-view mirror, connected therewith, is adjusted to a driver-specific stored value, for which purpose a position signal is needed.
Potentiometers are used in simple electrical adjusting drives, if a position signal is required for controlling such a drive. In such adjusting drives, the driving wheel, for example a toothed wheel, meshes with a counter-toothing of the sub-assembly to be adjusted, which has two end positions. Slide resistor and sliding bow or slider of the potentiometer are, in potentiometers known from practice, securely connected on the one hand to the driving wheel and on the other hand to its base.
In order to obtain a position signal which is of some use, such known driving wheels have to be brought manually into one of the two end positions and mounted in such a way that the toothed wheel does not twist. Where space is tight, it is almost impossible, if not completely impossible, during installation to bring a toothed wheel into engagement with the counter toothed wheel without twisting. Even where this succeeds, the tolerances of the driven sub-assemblies here remain out of consideration, such that the adjustment is so imprecise that it cannot be designated as calibration.
It is thus the object of the present invention to create a drive device for an adjustable vehicle mirror using a potentiometer and to create a potentiometer itself, which are able to be standardized or calibrated with minimum technical outlay according to a method which is as simple as possible.
This object is achieved according to the invention by the features of the main claim and of the coordinated claim.
The drive device according to the invention for an adjustable vehicle mirror has at least one fixed portion and a mirror support, pivotable relative to the fixed portion by means of at least one driving motor and at least one driving toothed wheel, and a potentiometer to generate a signal indicating the pivoting angle between the fixed portion and the mirror support. The potentiometer here has at least one slide resistor and at least one slider or sliding bow, one of these two elements being securely connected to a base portion connected to the fixed portion, and the other of the two elements being connected via a slip clutch to the driving toothed wheel or to a swivel part co-operating with the driving toothed wheel. What is essential is that one of the two elements is connected via the slip clutch to the driving wheel or swivel part or the base portion, and the stops and counter-stops provided on both the elements carry the respective element along when first adjusted, such that this element is brought, exceeding the slipping moment of the slip clutch, into the positions corresponding to the end positions of the vehicle mirror to be adjusted. Thus the potentiometer can be installed in any position and the calibration can be undertaken quickly and easily when it is first put into operation. This is a purely mechanical and nevertheless very exact calibration, since it corresponds to the actual end positions of the mirror or mirror support to be adjusted, irrespective of their variations in dimension.
In a preferred embodiment of the invention, the slider is connected by means of a slip clutch to the driving toothed wheel or the swivel part and the slide resistor is securely connected to the base part and the base part has a nose which co-operates with stops of the slider. This arrangement is particularly advantageous because of the type of electrical connections and the particularly simple production and assembly of the parts.
As a development of the invention, the slider is a stamping which is circular in its basic shaper, and which comprises a flat section and at least one arcuate spring band bent out of the plane of the sector, the flat section being connected via the slip clutch to the driving toothed wheel or the swivel part, and having in addition two cutting edges which are oriented substantially radially and which form the stops. A stamped part of this kind can be produced in a single pressing stroke, is thus cheap and fulfils a plurality of functions simultaneously, slider, spring and slip clutch.
The slip clutch can here be formed from a central journal, forming the rotational axis of the driving toothed wheel or swivel part, and an internal toothing, the internal toothing being-a component part of the small metal plate forming the slider or of a clamping ring fixing the slider, which are pressed onto the journal. Thus the slip clutch is produced practically automatically during assembly. The danger of xe2x80x9cwearing outxe2x80x9d does not exist, since it only slips during the initial calibration and otherwise is not stressed.
The potentiometer according to the invention is constructed in a particularly simple manner and is thus inexpensive and can be used for mass production. In particular it is suitable for drives which have to be constructed particularly small and in which the space is very tight.
The drive device according to the invention with the potentiometer according to the invention can be calibrated in a particularly simple process. For this purpose, the base part with the driving toothed wheel or the swivel part is installed together with the other drive elements, generally one or more electromotors with a step-down gear, in any position and connected electrically, it being thereby possible to carry out the fitting also automatically without special arrangements, thus saving time. After assembly, the standardization or calibration can be carried out without having to undertake any manual adjustment, either immediately or not until the vehicle is used for the first time. To this end the adjusting drive or the adjusting drive device is first switched in the one direction until the mirror support reaches its end position, generally predetermined by its installation. If, beforehand, stop and counter-stop of the potentiometer meet one another (then the potentiometer is already located in its end position), one of the elements slide resistor or slider is taken along against the force of the slip clutch, until the sub-assembly, i.e. the mirror support, has also reached its end position. Since it can be assembled in any way, this happens either when the first end position is reached or when the second end position is reached.